I encountered the same problem you, and I found a method to avoid such error, but I don’t know whether it has any negative effects.
1. In “Plugin–>Editor”, select this plugin to edit.
2. In file “featured-images-for-categories/featured-images-for-categories.php”, search for “wpfifc_remove_option_when_post_deleted”.
3. Comment the whole line, look like this:
/*add_action( ‘delete_post’, array($this, ‘wpfifc_remove_option_when_post_deleted’), 10);*/
At least there’s no more such annoying errors again. ??